Electric arcs can occur inside voltage switch gears as a result of insulation failure or human error. The pressure from an electric arc is developed from two sources: the expansion of the metal in boiling, and the heating of the air by passage of the arc therethrough. Copper expands by an important factor (67000 times) in vaporizing. This accounts for the expulsion of near-vaporized droplets of molten metal from the arc; these droplets can be propelled for important distances (up to 10 feet). The pressure also generates plasma outward from the arc for distances proportional of the arc power. One cubic inch of copper vaporizes into 1.44 cubic yards of vapor. The air in the arc stream expands in warming up from its ambient temperature to that of the arc (about 35000.degree. F).
Therefore, the arc can cause flash burns to the nearby personnel, or falls and collisions if and when they propelled by the pressure developed by the arc.
Aother consequence of arcs in switchgears is structural damage to nearby equipment or walls.
Previous methods of protection used multi-point latch systems in arc-proof doors. These systems utilize captive panel screws to bolt the door to .the frame on both vertical sides and top. Some systems also use hooks on the door and pins on the frame.